质谱法定量研究气相中二价锰离子与环糊精的非共价复合物

Investigation on Non-Covalent Complexes of Cyclodextrins with Mn2+ in Gas Phase by Mass Spectrometry

为了探索+2价过渡金属锰离子与环糊精(CD)的非共价作用,采用质谱法(ESI-MS)研究了Mn^2+与α-环糊精(α-CD)、β-环糊精(β-CD)、γ-环糊精(γ-CD)、2,6-二甲基-β-环糊精(DM-β-CD)或2,3,6-三甲基-β-环糊精(TM-β-CD)气相中的非共价复合物。一级质谱实验结果表明,Mn^2+可以在气相中与α-CD、β-CD、γ-CD、DM-β-CD或TM-β-CD结合,形成配合比为1∶1的非共价复合物,二级质谱进一步确认了复合物的形成。碰撞诱导解离实验显示,[DM-β-CD+Mn]^2+(m/z=693)前体离子在较高的碰撞能量时(20 eV),不仅出现丢失甲基化葡萄糖单元中性分子的A系列碎片离子,甲基化葡萄糖单元也可能获得质子,并发生进一步碎裂,产生失去水分子的系列分子离子峰。采用质谱滴定法定量测定了四种复合物[Mn+α-CD]^2+、[Mn+β-CD]^2+、[Mn+DM-β-CD]^2+和[Mn+TM-β-CD]^2+的解离常数。结果表明,Mn^2+与α-CD、β-CD、DM-β-CD和TM-β-CD复合物的解离常数(Kd1)分别为4.9、8.8、9.9、6.2μmol/L。

To investigate the non-covalent interaction between cyclodextrins(CD)and manganese ion(Ⅱ),electrospray ionization mass spectrometry(ESI-MS)was employed to examine the complexes of Mn^2+withα-cyclodextrin(α-CD),β-cyclodextrin(β-CD),γ-cyclodextrin(γ-CD),heptakis(2,6-di-O-methyl)-β-CD(DM-β-CD)or heptakis(2,3,6-tri-O-methyl)-β-CD(TM-β-CD)in gas phase.The binding of complexes was further confirmed by collision-induced dissociation(CID).CID results also demonstrated that the decomposition of precursor[DM-β-CD+Mn]^2+(m/z=693)proceeded in such a direction which consisted of consecutive losses of mass 96(series A)at collision energy of 20 eV.Meanwhile,the 2,6-di-O-methyl glucose unit could obtain proton to cleave followed by a consecutive losses of mass 18(H2O).The dissociation constants(Kd1)of four complexes([Mn+α-CD]^2+,[Mn+β-CD]^2+,[Mn+DM-β-CD]^2+and[Mn+TM-β-CD]^2+)were determined by mass spectrometric titration.The results showed that Kd1 were 4.9,8.8,9.9 and 6.2μmol/L for the complexes of Mn^2+withα-CD,β-CD,DM-β-CD and TM-β-CD,respectively.